Amplifier circuits



Patented July 7, 1925.

UNITEDQS-TA'TES PATENT OFFICE.

ROBERT C. MATHES, OF NEW YORK, N. Y., ASSIGNOR TO 'WES 'IERN ELECTRIC GOM- PANY, INCORPORATED, OF NEW YORK,- N. Y., A CORPORATION OF NEW YORK.

AMPLIFIER CIRCUITS.

Application filed November 12, 1919. serial flo. 387,565.

To all whom it may concern:

Be it known that 1, ROBERT C. MATHEs; a citizen of the United States, residing at New York, in the county of Bronx, State of New York, have invented certain new and useful Improvements in Amplifier Circuits, of which the following is a. full, clear, concise, and exact description.

This invention relates to vacuum tube circuits and more particularly it: relates to amplifier-circuits, for repeating speech frequencies without distortion.

In the patent to Colpitts No. 1,128,292, granted February 16, 1915, there is shown a pair of vacuum tubes, connected in opposition or push-pull relation, as an electric wave amplifier. The push-pull connection of vacuum tubes will herein indicate the relationship shown, for example, in the above patent, where the input or control electrodes are so connected to an incoming line that one control electrode is made positive when the other is made negative, and the output circuit of the tubes are so connected to anoutgoing line that the increase of current in one 1 output circuit has a similar effect upon the outgoing line as a simultaneous decrease of current in the other output circuit. It has been found that the repeating qualities of such apparatus are improved by utilizing suitable impedance elements in the output circuits of the tubes. Previously, it has been customary in selecting vacuum tubes for such push-pull amplifying circuits to secure tubes having as nearly identical electric characteristics as possible because if the tubes do not have identical characteristics a certain amount of distortion or imperfection of operation results. Likewise, imperfect operation results fromunbalance, that is, the dissimilarity of the correspondin branches of the divided circuit associate with the vacuum tubes. In practice, it is very difficult to secure'vacuum tubes which are identical in all respects. Even if two specimens of a lot were identical in characteristics, much time Would be consumed in exhaustive tests to select that particular pair and, moreover,,itis impractical to exactly balance two sides of the divided circuit. "By the use of this invention, the results secured with slightly unbalanced circuits or tubes are very much improved. In a system operating in accordance with this invention, it

is desirable that for the particular frequency" or frequenciesto be repeated an increase of space current; through one tube will causean equal and simultaneous decrease of current through the other tube. The impedance elements to be added according to this invention are designed with this end in View.

In its specific aspect, hereafter described indetail, this invention comprises a pushpull amplifier circuit in which high im-- pedance elements, such as choke coils are inserted in the direct current branches of theoutput circuits of the amplifiers. It has'been found that with such an arrangement, there is substantially no distortion of the incomingsignals and-the system acts in a manner which would be expected if the input-out- 5 put current characteristics of the tubes was linear over the whole Working range of amplitude.

It has also been found advantageous to employ such a circuit arrangement in a multistage amplifier set, each stage of which is of the push-pull type.

This invention will be better understood by reference to the following detailed description taken in connection with the ac-.

the cathode 8 of tube 4 is a choke coil 15.

Similarly connected between the grid 16 and the cathode 9 of tube 5 is a second choke coil 17. These impedances l5 and 17 are connected across the incoming line 18 and serve to impress any incoming signals on tubes 4 and 5. The connection is such that incoming waves that make one of the grids positive make the other grid negative so that when the impedance of one of these tubes increases the impedance of the other tube decreases. I

The direct current branch of the output circuit of tube 4 is traced from anode 21. high impedance 22, wire 23, battery 13, through ground to cathode 8. Similarly, the

direct currentbranch of the output circuit for tubefi may be traced from anode 24;,

high impedance 25, wire 23, battery 13, through ground to cathode 9. Choke coils 22 and 25 should be designed to offer a very high impedance to currents of the frequencies which are to be repeated. A substantially constant current will therefore flow through the branches of the output circuits which include these coils.

The amplified signals from tubes 4 and 5 will therefore be confined to the paths containing condensers 27 and 28 and will consequently be impressedacross the terminals of impedances 29 and 30 upon the grids 31 and 32 of tubes 6 and 7.

The direct current branch of the output circuit of tube 6 is traced from anode 33, impedance 34, wire 35, battery 13, through ground to cathode 10. The direct current ranch of output circuit of tube 7 is traced from anode 36, impedance 37, wire 35, battery 13, through ground to cathode 11. Choke coils 34 and 37 should be designed to offer a very high impedance to the currents of the frequencies which are to be repeated so that substantially constant current flows through these coils. The amplified signals from tubes 6 and 7 will therefore be confined to the circuit whichincludes condenser 38, primary winding 39 of transformer 40, and condenser 41. Even though the characteristics of tubes 6 and 7 are not identical, the action of the impedances 34 and 37 in confining the amplified alternating cur-.

rents to the circuit traced above, tends to cause the increase in current through one tube due to a change in its grid voltage to be equal to the decrease of current in the other tube. Hence the effect induced in the secondary winding of transformer 40 for the positive half cycle of a symmetrical in coming wave tends to be identical in magnitude with the effect produced by the succeeding negative half cycle. With these impedances 34 and 37 omitted, this equality would not exist and distortion would occur. It follows, therefore, that the amplified impulses impressed on outgoing line 43 by transformer 40 are faithful reproductions in amplified form of the signals coming in from line 18.

Condensers 44 and 45, which are inserted between the incoming line and the input of the amplifier set, serve to isolate. the repeating apparatus from the effects of direct current voltage sources which may be included in line 18. These condensers 44 and 45, when used, are preferably of large capacity so as to offer low impedance to alternating currents passing therethrough. In case it is desired to prevent the repeating appara tus from amplifying signals of frequencies above the essential range to be repeated, inductances 46 and 47 may be included in series with line 18 in order to choke out these" undesired frequencies while allowing the es sential range of frequencies to pass therethrough.

It is to be noted that the cathodes and the midpoints of impedances 15 and 17, 22 and 25, 29 and 30 and 34 and 37 are grounded. This grounding is to prevent any undesired transfer of energy from one part of the repeater circuit to another part through capacities to ground from causing the apparatus to howl or sing.

It is to be understood that this invention may be variously modified without departing in any way from the spirit of this invention as defined in the appended claims.

What is claimed is:

1. In an electric system, a plurality of oppositely connected vacuum tubes each having a cathode, and a connection to ground for said cathodes for preventing said tubes from singing.

2. An amplifying system comprising a plurality of oppositely connected vacuum tubes, each comprising a cathode, an anode, and a control electrode, a connection between two of said cathodes and ground, and a symmetrical conducting path from ground to each of said control electrodes for preventing said tubes from singing.

3. An amplifying system comprising divided input and output circuits, electrodes connected to said output circuits, means for producing two ionized streams, said streams being connected in opposition, a control element for controlling each of said streams, a connection between one of said electrodes and ground, and a symmetrical conducting path from ground to each of said control elements for preventing energy from said output circuits from being fed back into said input circuits.

4. An amplifying system comprising a plurality of oppositely connected vacuum tubes, each comprising a cathode. an anode and a control electrode a connection between two of said cathodes and ground, and a symmetrical conducting path from ground to each of said control electrodes, each of said paths containing an inductance of high impedance for waves of all frequencies to be amplified. Y

5. An electric system comprising a plurality of vacuum tube repeaters connected in opposition, each of said vacuum tubes having a cathode, an incoming line, and a conducting path in shunt to said line comprising two similar impedances, said cathodes and the common point of said impedances being grounded.

6. In combination, an incoming line, a condenser and a choke coil in series with each side of said line, two vacuum tube repeaters connected in opposition and each comprising a cathode, an anode and a control electrode, said control electrodes being individually connected to said line.

7. An electric system comprising a plurality of op sitely connected vacuum tubes each of sa1 tubes comprising a cathode, an anode and a control electrode, a symmetrical conducting'path from (ground to each of said control electrodes, an a symmetrical conducting path from ground to each of said anodes.

trode, a symmetrical conducting path from.

ground to each of said control electrodes, and a symmetrical conducting path from ground to each of said anodes, each of said paths comprising an inductance of high impedance for waves of all frequencies to be repeated. I

10. A multi-sta'e vacuum tube set, each of a plurality 0% said stages comprising means for producing two electron streams, the streams of each of said stages being connected in opposition, and coupling means between two of said stages comprising a condenser.

11. A multi-stage vacuum tube set, each of a plurality of said stages comprising means for producing two electron streams,

the streams of each of said stages being connected in opposition, and coupllng means between two of said stages comprising a high impedance shunt and a series condenser.

12. A multi-stage repeating set comprising two vacuum tubes connected in opposition in each of a plurality of said stages, P.

said path comprising each of said vacuum tubes having an anode a cathode and a control electrode, one 0 said stages having an output circuit comprising a path between said anodes of high impedance to'alternating current, and low impedance to direct current, and a path between itsanodes of high impedance to direct current, and low impedance to alternating current.

13. A multi-stage repeating set comprising two vacuum tubes connected in push-pull relation in each of a plurality of said stages,

one of said stages having an output circuit having certain portions thereof common and other portions individual to the tubes of thestage, an inductance in each of said individual portions, and a by-pass around said inductances comprising a condenser.

14. A multi-stage repeating set comprising two vacuum tubes connected in opposition in each of a plurality of said stages, each of said stages having an output circuit with ortions in common and other portions individual to'the tubes in one stage, a high impedance in each of said individual portions, a source of voltage, and a connectionfrom a point intermediate said impedances in each of a plurality of said stages to said source.

15. A vacuum tube repeater comprising two vacuum tubes connected in opposition, lnput and output clrcuits therefor, said .out-

put circuit comprising a simple circuit for alternating currents, a divided circuit for direct currents, and a choke coil in eachbranch of said divided circuit, said choke coils having separate cores.

16. A vacuum tube repeating system comprising two vacuum tubes connected in opposition, an output circuit for said tubes having portions individual and other portions common to said tubes, and a high inductance in each individual portion of said output circuit, said inductances being de-' signed and positioned to have negligible mutual inductance therebetween. l

17 A vacuum tube repeating system com prising two vacuum tubes connected in opposition, .an output circuit for said tubes having portions individual and other portions common to said tubes, a high inductance in each of said individual portions, said inductances being adjusted and positioned to have negligible mutual inductance therebetween, an outgoingline, and a transformer for impressing the repeated currents upon said line. i

18. A vacuum tube repeating system comprising two vacuum tubes connected in opposition, input and output circuits therefor, each of said tubes comprising an anode, a cathode and a control electrode, means for impressing an alternating current wave upon said control electrodes, a direct current ath between said cathodes and said anodes, ortions in common and other portions individual to said tubes, and means in said ath presenting substantially the same hig impedance to alternating currents when said anodes are both positive with respect to a point in said common tive and the other negative for alternating currents with respect to said point.

19. In combination, a push-pull repeater,

' a second push-pull repeater, and a condenser coupling for connecting the output of said first repeater to the input ofsaid second repeater.

20. In combination, a push-pull repeater, a second push-pull repeater, each of said repeaters comprising a plurality of anodes and a plurality of cathodes, a connection from an anode of the first repeater to the control electrode of the second repeater comprising a capacity, a connection from a second anode of the first repeater to another control electrodc of the second re eater comprising a second capacity, and s unt paths connecting corresponding terminals of-said capacities, each of said paths'comprising a high impedance.

21. An electric system comprising divided input and output circuits, electrodes connected to said output circuit, a common source of voltage for producing two ionized streams in push-pull relation between said electrodes, and a retard coil of high impedance to alternating currents connected in series with said source in each of the separate,

portions of said output circuit, said retard coils being designed and positioned to have negligible mutual inductance therebetween.

:22. A multistage amplifier set comprising a push-pull repeater in each of a plurality of said stages each of said push-pull repeaters having a control electrode and an output circuit, a common source of voltage for said output circuits aretard coil of high impedance to alternating currents connected between said source and each of said pushpull repeaters, and means for preventing direct current voltage from said source as applied to one stage from being impressed upon the control electrodes of the succeeding stage.

23. In combination, a plurality of vacuum tubes connected in push-pull relation, a common source of space current for said tubes, and means to prevent alternating current from one side of said repeater from flowing into the portion of the space current circuit common to both sides of said repeater.

In Witness whereof, I hereunto subscribe my. name this 3rd day of November A. D., I

ROBERT C. MATHES. 

